Pronoun "you" refer to a group?

Hi. In the following writing, would you say the use of the pronoun "you" to refer to a group of people is correct? Then which word should we use for the underlined part? Would you say that we could use the word "yourself" instead of "yourselves" as I think it should be.

eg,

(made-up context)

Okay, guys, you know that they have done a great job in organizing the event this year. And compared to them, I would say your event this year was an event that left much to be desired. I think you know what are the things that need to be improved (upon?). If you don't know what some of them are, I suggest you try to find out what they are yourself (yourselves?) as soon as possible.